Sensors Cambridge IGCSE Computer Science (9–1) revision
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In plain words
A sensor is an input device that measures something about the world around it, and keeps measuring. It is how a computer knows that a room is too hot, a door has opened or a tank is nearly full.
The trick in the exam is to choose the right sensor for the situation, and to say what it measures.
6 things to know
- A sensor measures a physical property of its surroundings and sends the data to a microprocessor. The readings are analogue, so they are converted to digital first.
- Temperature sensor: how hot or cold. Light sensor: how bright. Humidity sensor: the amount of water vapour in the air. Moisture sensor: the amount of water in soil.
- Pressure sensor: a force pressing on it, such as someone standing on a mat. Level sensor: how high a liquid is in a container. Flow sensor: how fast a liquid or gas is moving through a pipe.
- Gas sensor: the amount of a gas, such as carbon monoxide. pH sensor: how acidic or alkaline a liquid is.
- Infra-red sensor: heat given off by a body, or a beam being broken, used to detect movement. Proximity sensor: how close an object is.
- Acoustic sensor: sound levels. Accelerometer: acceleration, movement and tilt. Magnetic field sensor: the presence and strength of a magnetic field.
Worked example
A greenhouse must be kept warm, with damp soil and enough light. Which sensors does its control system need?
- Warmth: a temperature sensor.
- Damp soil: a moisture sensor, pushed into the soil.
- Enough light: a light sensor.
Tips and tricks
- Moisture is water in soil. Humidity is water vapour in the air. Mixing them up is the most common slip in this topic.
- Always say what the sensor is used for in that situation, such as "a pressure sensor to detect a car over the entrance".
It lands in your notebook with its questions as flashcards.
Sensors: 6 questions and answers
These are the quiz’s questions. Do the quiz first, then come back here for the ones that got you.
What does a sensor do?
It sends its readings to a microprocessor.
Which sensor measures the amount of water in soil?
Humidity is water vapour in the air.
Which sensor would detect that a phone has been tilted?
It measures acceleration and tilt.
Which sensor would measure how full a water tank is?
A flow sensor measures how fast water moves through a pipe.
Why do the readings from a sensor need converting before a computer can use them?
An analogue-to-digital converter does this.
Which sensor would be best for detecting an intruder walking through a doorway?
It detects body heat or a broken beam.
Quiz
6 questions
Tap an answer and you’ll see straight away whether it’s right, and why.
Worksheet
2 questions, 5 marks. Write your answers on paper, then check them.
Sensors
Cambridge IGCSE Computer Science (9–1) 0984 · 5 marks · papermunch.org
Name ______________________________ Date ______________
A car park barrier must rise when a car arrives. Name a suitable sensor and state what it would detect.[2]
Show answerHide answer
A pressure sensor, to detect the weight of a car on the road. (Or an infra-red sensor, to detect a car breaking a beam. Or a proximity sensor.)
Name three sensors that could be used in a system that controls a fish tank, and state what each measures.[3]
Show answerHide answer
A temperature sensor for how warm the water is. A pH sensor for how acidic the water is. A level sensor for how high the water is.
Answers: Sensors
- 1. A pressure sensor, to detect the weight of a car on the road. (Or an infra-red sensor, to detect a car breaking a beam. Or a proximity sensor.)
- 2. A temperature sensor for how warm the water is. A pH sensor for how acidic the water is. A level sensor for how high the water is.